Wooden trussed structural systems, such as frameworks, bridges, floors

ABSTRACT

A wooden trussed structure includes beams which are constructed from at least three elementary planks, nailed together. The plank located in the central part is offset relatively to the ends of the lateral planks, so as to form thereat, tenons and/or mortises for inserting, at the junction forming a node, a panel-type reinforcement, positioned in the core, and wherein the shearing surfaces correspond to the lateral surfaces at each node. The panel includes a wooden structural element such as a micro-lath or plywood as a plate-type solid web.

TECHNICAL FIELD

[0001] Wood is a material which is very widely used in construction, and with which it is possible to produce a whole series of bearing systems having their own specific mechanical properties and capable of withstanding all levels and types of load.

[0002] The various bearing systems made of wood are posts and beams, trussed systems, jointed systems, portal frames, latticeworks of beams, shelves and elements operating as plates.

[0003] Amongst all these structural systems, the trussed system is the most universal because it is capable of supporting very high loads, while at the same time being very simple to construct. By way of indication, the trussed system is at the heart of the roof-truss systems used in Europe which were developed as long ago as the 12th century and which are still in use today.

[0004] Wooden trussed systems can be classified into two broad families illustrated schematically in the appended FIGS. 1 to 6.

[0005] The first system, known as the “system with parallel members”, illustrated in FIGS. 1 to 3, is used, for example, for bridges or horizontal flooring systems.

[0006] A system such as this is made up of:

[0007] an upper member or purlin (1),

[0008] a lower member or purlin (2),

[0009] posts (3) and possibly uprights (M),

[0010] diagonals (4).

[0011] The assembly thus produced rests on at least two bearers (5). To reduce internal forces, bearers can sometimes be added within the system, but this is not always possible.

[0012] “Triangular” systems, as illustrated in FIGS. 4 to 6, are generally used to produce frameworks for roofing, and allow the roofs to be pitched.

[0013] The elements involved in producing such systems are made up of one or two principal rafters (6), of a tie (7), of diagonals (8) and possibly of one or more uprights (9).

[0014] Such assemblies rest on bearers (5) arranged at each end of the tie (7).

[0015] The invention relates to this technical field and is concerned more specifically with producing a new type of bearing system both in the case of systems with parallel members and in the case of triangular systems which, while at the same time having good mechanical properties, allow a reduction in the production costs and can be readily adapted to suit the characteristics desired for each specific application (load to be withstood, dimensions of the system, etc).

PRIOR ART

[0016] One of the main problems posed in the context of producing either systems with parallel members or triangular systems, is that of being able to absorb the maximum flow of force which is localized at the bearers and generates maximum tension and compression in the bars connected to the first node by the various elements which transmit the forces to the bearer.

[0017] Conventionally, the first node, in the case of frameworks, connections, ties (7), principal rafters (6) and diagonals (8), is made using pieces of solid wood or glued laminated timber, according to the requirements in terms of cross section, and the node is produced using metal fittings in the case of systems with high inertia, or even sometimes simply glued in the case of flooring systems of lower inertia.

[0018] A great many proposals have been made with regard to producing the node that assembles trussed wooden systems, whether these be systems with parallel members or triangular systems.

[0019] Among these solutions, mention may be made of the one featured in U.S. Pat. No. 4,891,927 which proposes reinforcing the trussed node using an internal metal connector equipped with nails or pins which are driven into the members which are made up of two layers. A solution such as this is extremely expensive because it entails force-fitting the node at the factory, which does away with the possibility of assembling it by hand on the actual site, in a way that can be readily adapted to suit the constructions to be built. Furthermore, it is not entirely satisfactory because the force on the node depends on the cross section of the wood.

[0020] German patent DE 3 910 027 proposes a solution with two-layer purlins and a trussing system with diagonals made of planks (5) or composite beams positioned in the web. Such a solution does not, however, allow the most heavily loaded nodes to be reinforced.

[0021] In other sources, it has long been proposed, as is apparent from U.S. Pat. No. 2,886,857, for the purposes of reducing the cost of manufacture of trussed systems, for the beams involved in producing such systems to be produced not from large cross-section solid wood or from glued timber, which are relatively expensive, but using structures consisting of planks nailed together to make up larger cross sections from wood of smaller cross section which is therefore more economical.

[0022] Such a structure using nailed planks makes it possible to lower the cost price and make up a large cross section without having the problems of solid wood such as deformation and cracking.

[0023] Furthermore, with thin planks, for example of the order of 30 to 50 mm thick, it is possible to carry out artificial drying under conventional conditions.

[0024] In addition, as the wood is nailed together in the dry state, there is no longer any deformation of the made-up section.

[0025] The solution described in the aforementioned patent does, however, have a number of drawbacks as far as reinforcing the nodes is concerned and cannot be tailored equally well to the two broad families of wooden trussed systems known as “systems with parallel members” and “triangular systems”.

[0026] First of all, this solution has, in the central layer, planks which are nailed between the two planks of the other members. This nailing tends to cause the central plank to split because the distance to the loaded edge, parallel to the fibers, is too short. This central web made of planks therefore exhibits poor performance at its points of assembly.

[0027] Next, the fact of having a succession of planks in the central web makes it possible to create the inertia by spacing the outer members apart, but since this web of planks is discontinuous in the transverse direction, it cannot support either the bending moment or the local shear force generated by the two inner beams, for example the compressed diagonal and the tensioned upright. It does not therefore reinforce the node with respect to bending and local shear which are significant mechanical components in the node system.

[0028] Finally, to end with, this central web is forced to fill the entire space between the outer members because it has rigidity only along one axis, its longitudinal axis. This web therefore constitutes a global zone between the outer members, and does not provide local reinforcement tailored to one single connecting node. It does not allow the node to optimized either in terms of performance (weakness to nailing) or in terms of economizing material (solid zone, with respect to local zone).

SUMMARY OF THE INVENTION

[0029] Now, it has been found, and this is what is the subject of the present invention, that it is possible to produce structural systems either with parallel members or in triangular form, of the type illustrated in FIGS. 1 to 6, in which the various elements—purlins, diagonals, posts, ties, uprights, principal rafters—which, in the remainder of the description, will be known by the common term of “beam”, make it possible, in a single way, to reinforce the nodes that join these elements together, each beam being constructed from planks nailed together to make up larger cross sections.

[0030] In general, in wooden structural systems according to the invention, the various beams are produced actually on site by nailing at least three elemental planks, nailed together, and are characterized in that:

[0031] the three elemental planks that make up each beam are of the same thickness;

[0032] the plank located in the central part:

[0033] being offset with respect to the ends of the lateral planks, this being in such a way as to form, at this point, tenons and/or mortises making it possible to include, at the junction zones forming nodes, a reinforcement of the “panel” type, which is positioned in the web, and the shear surfaces of which correspond to the lateral surfaces at each node, said panel being made up of a structural wooden element of the “thin strip” or “ply” type allowing the bearing zone to be stiffened operating, like a solid rib of the “plate” type,

[0034] consisting either of a continuous plank or of elemental planks placed end to end or spaced apart so as to form a mortise capable of accommodating a reinforcement of the “panel” type or, possibly, in the case of nodes which do not require reinforcement, a simple tenon formed by the end of the central plank of a beam associated with the system.

[0035] A solution such as this allows greater forces to be withstood, the panels interfaced at the junction zones (nodes) supplementing the nailing zones.

[0036] Furthermore, the solution according to the invention also makes it possible to reduce the bending moments in the joint because the reinforcement itself absorbs bending given that the “plate”-type reinforcement has very great rigidity because it works in both directions of its plane. A reinforcement such as this makes it possible to support the shear forces of the internal beams, such as, for example, the shear force between a compressed diagonal and a tensioned beam, at the node, relieving the mechanical stress in the outer beam by a corresponding amount.

[0037] This reinforcement may be more or less isotropic according to the forces to be supported.

[0038] As mentioned earlier, the beams involved in producing a system according to the invention will consist of at least three layers, the reinforcements therefore being positioned in the central layer, exposing the nails that pass through the reinforcement to two lots of shear by comparison with reinforcements exposed on the outside of the system as is often the case.

[0039] According to one particular embodiment which will become apparent from the remainder of the description, particularly in the case of a system with parallel members, the two end posts will also consist of three layers nailed together, the central layer not consisting of a plank but consisting of a structural wooden element of the thin strip type protruding from the ends of the two lateral planks and toward the inside of the structure so as to form tenons capable of receiving the mortises of the other beams of the system.

[0040] Aside from beams comprising three elemental layers, it may be envisioned for beams of five layers or more to be produced, it being possible for the reinforcement to be positioned either solely in the central position, or possibly duplicated then positioned in layers (two) and (four).

[0041] In other words, in such an instance, the structural system according to the invention is characterized in that the number of planks involved in making up each layer is an odd number and is greater than three, for example five, a reinforcement being positioned at each node in the even-numbered layers.

[0042] The reinforcing ribs or plates are arranged at least at the bearing zones where the forces are at their highest. As an option, as the internal forces are lower in the uprights and diagonals, assemblies of the trussed system may possibly be produced in the conventional way using a simple assembly of the “tenon/mortise” type, the tenon being formed by offsetting the central plank outward and the mortise being formed by the space between two elemental planks that make up the central plank.

[0043] It is, however, advantageous also to reinforce these zones by fitting a reinforcement plate at this point to make it possible directly to absorb shear between the compressed diagonal and the tensioned post, or vice versa.

[0044] At the joining regions, the reinforcement or rib is fixed along its entire periphery to the other beams (ties, principal rafters, uprights or diagonals) simply by nailing, which is the most economical solution and has the advantage of being semi-rigid, allowing the entire plate to be stressed following deformation of the edge connectors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The invention and the ensuing advantages will, however, be better understood by virtue of the remainder of the description which is illustrated by the appended diagrams in which:

[0046] FIGS. 1 to 3 and 4 to 6, as already stated, illustrate the general structure of, on the one hand, systems with parallel members and, on the other hand, triangular systems that can be produced in accordance with the invention;

[0047]FIG. 7 is a schematic view in elevation of a system with parallel members produced in accordance with the invention;

[0048]FIG. 8 is a detailed exploded perspective view of the ringed region in FIG. 7, showing how the assembly nodes are produced in the region of the bearer;

[0049]FIG. 9 is a schematic perspective view showing a framework produced in accordance with the invention with the various elements nailed together;

[0050]FIG. 10 is an exploded perspective view of the production of the nodes in the region of the end bearing zone and of the central upright with the tie and the diagonal of the framework.

EMBODIMENT OF THE INVENTION

[0051] In order to produce these structures, the elemental planks involved in making each beam are solid planks with a cross section generally of between 10 and 30 cm wide by 3 to 8 cm thick.

[0052] For structures capable of having great strength, individual planks may be made up of larger sections.

[0053] The length of said planks may vary according to the systems to be produced and will, for example, be between four and eight meters.

[0054] The concrete embodiments which follow will allow a better understanding of the invention.

[0055] Embodiment of a System with Parallel Members

[0056] A system such as this is of the type featured in FIG. 1.

[0057] To produce a system according to the invention, illustrated by FIGS. 7 and 8, all of the beams involved in making it, namely the purlins or members (1) and (2), the posts (3), diagonals (4) and intermediate uprights (M) that the system comprises have the following structure.

[0058] As regards the horizontal members or purlins (1) and (2) and the diagonals (4) and uprights (M) (the uprights are not depicted in FIG. 8), each beam consists of three elemental planks (10,11,12). The intermediate plank (10) is offset with respect to the ends of the lateral planks (11, 12) and, in this particular instance, this is by a distance of about 50 cm, thus allowing a recess forming a mortise (13) to be formed at each end.

[0059] The diagonals (4) are produced in a similar way from three planks and also have a mortise at their end.

[0060] The internal uprights (M) are produced in a similar way.

[0061] For its part, the post (3) consists of two outer planks (14) between which is inserted, over its entire length, a third plank (15) which is intended to form the reinforcement of the panel type positioned in the web and which is formed of a structural panel of the thin strip type 4 cm thick, the outer planks (14) also being 4 cm thick.

[0062] This panel (15) protrudes from the lateral planks (14,15) at each end and forms a tenon 20 cm high thus corresponding to the width of the planks (10,11,12) of which the purlins are made, and 50 cm long corresponding to the length of the mortise (13) made at the ends of the beams that make up the purlins.

[0063] The various elements are joined together by nailing.

[0064] While in the example illustrated, the reinforcing plate (15) extends over the entire surface of the system at each end in the region of the bearers (5), it could possibly be envisioned for reinforcing plates to be produced only at each of the ends, the central part of the post (3) then consisting of an additional plank, set back from the ends of the lateral planks.

[0065] As regards the nodes (17) formed at the region of the diagonals, uprights, purlins, internal joint zones, the joint is also produced by inserting additional plates in the regions of the joints.

[0066] Each of the elements therefore comprises, in the region of the joining zone, a mortise intended to take the reinforcing element.

[0067] As an option, the assembly could be performed without a reinforcing element and the ends of the uprights (M) and diagonals (4) would have the shape of a tenon consisting of the central plank being offset outward while the purlins or members (1,2) would, along their length, have mortises obtained by making the internal plank (10) using elemental planks spaced apart by a length corresponding to the tenon at the ends.

[0068] Embodiment of a Framework

[0069] An embodiment such as this in accordance with the invention is illustrated in FIGS. 9 and 10 and corresponds to the general structure featured in FIG. 4, it being understood that structures of the type illustrated in FIGS. 5 and 6 could be produced in a similar way.

[0070] This structure is also produced from planks with a cross section of 20 cm×4 cm.

[0071] In this example, all of the zones of joining between the principal rafters (6), the tie (7), the diagonals (8) and the upright (9) comprise reinforcing panels denoted by the same reference (20).

[0072] As illustrated previously, all of the beams involved in producing such a system consist of three elemental beams (21,22,23) nailed together. At the ends, the central plank (21) is positioned set back from the ends of the lateral planks, so as to form in this region a mortise (24) capable of housing a reinforcing element.

[0073] In the region of the joint between the ends of the tie (7) and of the principal rafter (6), the reinforcing insert (20) is of triangular shape, the base of the triangle having a length of 700 mm, and the triangle being 400 mm tall.

[0074] At the node formed by the diagonals (8), the uprights (9) and the tie (7), mortises are provided at each of the ends of the diagonals (8) and uprights (9), this being by offsetting the internal layer with respect to the ends of the lateral planks, the mortise in the tie (7) for its part being obtained by making the central plank from elemental planks spaced apart.

[0075] As before, the various constituents are joined together by nailing and by the reinforcements (20) of the nodes, joined using a panel consisting of a structural wooden element of the thin strip type 4 cm thick.

[0076] Such trussed structural systems have numerous advantages over the solutions of the prior art, namely:

[0077] the possibility of being produced actually on site,

[0078] the possibility of making up a large section, and of doing so very economically,

[0079] the possibility of providing material (panels) only to allow the necessary nailing and to support the localized bending moment and shear of the internal beams arriving at the node, for example the shear generated by a compressed diagonal and a tensioned post, or vice versa.

[0080] Furthermore, the fact of producing such a structure using nailed planks to form the various beams involved in the system makes it possible to produce tenons and mortises simply by offsetting one layer with respect to the others.

[0081] In addition, the reinforcing panels positioned in the web of each beam make it possible to increase the area of the nailing zones reinforcing the structure. Such an interfaced panel also regulates the bending moments in the joint on the purlins in the case of a system with parallel members or a triangular system, because the reinforcement itself absorbs the bending; it thus absorbs the shear between the internal beams arriving at the node, mechanically relieving the stress in the outer beam. 

1. A system for trussed wooden structures, with parallel members or in the shape of a triangle, for producing frameworks, bridges, floors, consisting of beams (1,2,3;4,M)-(6,7,8,9) made up of at least three elemental planks (10,11,12,14,15)-(21,22,23) nailed together, characterized in that: the elemental planks that make up each beam are of the same thickness; the plank (10,15)-(21) located in the central part is offset with respect to the ends of the lateral planks (11,12,14)-(22,23), this being in such a way as to form, at this point, tenons (16) and/or mortises (13-24) making it possible to include, at the junction zones forming nodes, a reinforcement (15) (17) (20) of the “panel” type, which is positioned in the web, and the shear surfaces of which correspond to the lateral surfaces at each node, said panel being made up of a structural wooden element of the “thin strip” or “ply” type allowing the bearing zone to be stiffened, operating like a solid rib of the “plate” type.
 2. The structural system as claimed in claim 1, characterized in that the plank (10-15)-(21) located in the central part consists of elemental planks placed end to end or spaced apart so as to form a mortise capable of accommodating a reinforcement of the “panel” type.
 3. The structural system as claimed in one of claims 1 and 2, characterized in that the number of planks involved in making up each beam is an odd number and is greater than three, for example five, a reinforcement being positioned at each node in the even-numbered layers.
 4. The structural system as claimed in one of claims 1 to 3, characterized in that the reinforcing plate consisting of a structural wooden panel constitutes the central plank (15) of the beams that make up the posts (3) of a trussed structure with parallel members. 